In German Offenlegungsschrift No. 17 29 043, there is disclosed a calendering system for thermoplastic plastics material films. Such system comprises calender for producing the film and an embossing calender disposed subsequent thereto. The embossing calender comprises an embossing roller, a counter-roller having a resilient coating, and a pressure roller. All of these rollers are rotatably mounted in a displaceable frame.
In calendering systems for the production of films of, for example, polyvinyl chloride, the film is drawn off by a transfer arrangement in a ratio of substantially one to two immediately after leaving the calender.
After the drawing operation, the film passes into the embossing calender. The counter-roller, which is provided with a resilient surface coating, is forced, by the embossing roller, towards the drive roller, whereby all of the rollers are simultaneously caused to rotate.
During the embossing operation, it is particularly important that the film enters the nip between the counter-roller and the embossing roller at right angles to the plane containing the longitudinal axes of these two rollers. Before entering the nip, it is important that the film does not contact either the embossing roller or counter-roller.
To produce an extensive range of films on a calendering system, the system must be capable of embossing either of the two surfaces and of embossing both surfaces of the film. Hitherto, when it was desired to emboss the lower, rather than the upper surface, of a film, the system required substantial alteration. The change-over process necessitated complete dismantling of the embossing calender to ensure the proper direction of guidance of the film into the embossing nip, and to ensure that there was no prior contact of the film with either the embossing roller or the counter-roller, as described hereinbefore.
This change-over process meant that the calender line was out of commission for at least one working day.
To overcome the above-mentioned disadvantage, the invention disclosed in German Patent Specification No. 35 06 256 was devised. In such arrangement, the embossing roller, the counter-roller and the auxiliary roller are located in a displaceable frame. The frame is pivotable into a vertical location about a pivot point situated in the displacement path of the frame. Such device does, in fact, permit either surface of the film to be embossed as desired, without entailing time-consuming adaptation of the system. However, it is not possible, using such an arrangement, to emboss both surfaces of the film in a single production operation. To emboss both surfaces, the first surface is initially embossed and, the film then has to be fed to a second heating and embossing system.
In addition, a calendering system provided with twin embossing devices arranged in tandem has been disclosed for embossing both surfaces of polyvinyl chloride films.
In such an arrangement, the film is initially fed to a first embossing mechanism comprising an embossing roller, a counter-roller and an auxiliary roller. Such rollers are disposed in a generally horizontal array. The feeding of the film is effected by a calender through the intermediary of a transfer arrangement which comprises a plurality of rollers disposed adjacent one another. A second transfer system receives the film after it has been embossed on one surface and advances it on to a second embossing mechanism comprising an embossing roller, a counter-roller and an auxiliary roller. The rollers, in this latter arrangement, are disposed in a generally vertical array. The second surface of the film is thus embossed and a third transfer system receives the film now embossed on both sides, and advances it for any desired subsequent treatment.
Such a calendering system with two embossing systems in tandem with one another suffers from the disadvantage that it is necessary to provide a comparatively complex, cost-intensive, second roller frame having an additional auxiliary roller for the second embossing mechanism. In addition, it is only possible to emboss a single surface of the film in such an arrangement if the second embossing mechanism can be pivoted away from the path of travel of the film. In such circumstances, the film must pass from the final roller of the second transfer system direct to the first roller of the third transfer system. Inevitably, the film will sag further in this region in a disadvantageous manner. An additional disadvantage of this system is that it occupies a relatively large space. It will be apparent sufficient space must be available to pivot the second embossing mechanism out of the path of the film.